This invention relates to an improved vane-type fuel pump for delivering fuel, and particularly to an improved vane-type fuel pump for delivering fuel from a locomotive storage tank to a locomotive engine.
Diesel electric locomotives are fitted with various auxiliary electrical components which together make up the auxiliary electrical system. The auxiliary electrical system includes a DC motor driven, positive displacement fuel pump to deliver fuel to the locomotive engine. The pump is powered by the locomotive's 64 volt batteries during start-up of the locomotive, and by a 74 VDC auxiliary generator while the locomotive is running.
One design of positive displacement pumps that may be used as a locomotive fuel pump is the vane-type rotary pump. A vane pump can provide a relatively constant discharge pressure throughout a range of flow rates, and is fairly compact as well.
A vane pump includes a cylindrical pump chamber with a rotor mounted eccentrically within the chamber. The rotor incorporates vanes which define successive pumping chambers by maintaining contact with the perimeter wall of the housing at prescribed angular intervals throughout the rotation of the rotor. As the rotor turns, the volume of each pumping chamber alternatively increases and decreases due to the eccentricity of the rotor relative to the perimeter of the housing. In this way, fluid is alternately drawn into and discharged from each chamber, discharging a pulsating flow of fluid from the pump.
Owing to the eccentricity of the rotor relative to the circular housing, the distance between opposing walls of the housing measured through the center of the rotor varies as the rotor turns within the housing. Since the vanes must maintain contact with the housing wall throughout the rotation of the rotor, the vanes must adjust to this variation as the rotor turns.
As the required pump output volume is increased, greater eccentricity and/or higher rotor speeds are required. As the pump eccentricity is increased, the vanes must be adjustable over a greater range of lengths, and the rate of radial travel of the vane tip increases for a given rotor speed. As the rotor speed is increased, the rate of adjustment of the vane length must also increase accordingly.
An additional consequence of increased eccentricity and rotor speed of the vane-type pump is increased amplitude and frequency of vibrations associated with pulsations in the discharge from the pump. These vibrations can have a negative impact on the integrity of numerous structural components, including piping systems, seals, electrical connections, gauges, etc. In addition, the pump must be able to accommodate solid impurities in the fuel without jamming, breaking, or unduly wearing.
One result of these numerous and difficult design requirements are systems which include complex rotors and vanes having numerous moving parts. These complex designs in turn lead to high capital equipment costs, a high level of wear with respect to the equipment, and high maintenance requirements. The high level of wear and the high maintenance requirements are further aggravated by the fact that the pump must be operated continuously while the locomotive is running. The continuous use of the locomotive fuel pump also leads to additional maintenance problems with the DC drive motor. Frequent replacement of the brushes is required, and the internal parts of the DC motor are not easily protected from the operating environment of the locomotive. For example, the DC motor must be covered during normal cleaning of the locomotive to protect it from water damage.
Numerous vane-type pump designs are described in the literature. U.S. Pat. No. 1,019,995 to Seaman discloses a rotary pump having a cylindrical housing 20 with eccentrically mounted rotor assembly 16 mounted on concentric shaft 17. Vane 26 is carried on rotor 16 in openings 25 for sliding across the axis of rotor 16 as rotor 16 turns. Vane 26 has an elongated slot 31 which receives roller 29 which is carried on concentrically mounted stud 30 in cylinder 20. During operation, the ends of vane 26 are equidistant from the walls of cylinder 20. The distance between the vane ends and the walls of cylinder 20 varies constantly as rotor 16 rotates in cylinder 20. Rollers 27 are mounted in the ends of vane 26, and as rotor 16 is rotated, centrifugal force moves rollers 27 outwardly into contact with the walls of cylinder 20, providing a vane of varying effective length.
U.S. Pat. No. 1,749,121 to Barlow discloses a rotary pump having rotor 5 eccentrically mounted in housing 1. Rotor 5 has multiple slots 7 having rollers 8 disposed partially within. Rollers 8 are smaller in diameter than the width and depth of slots 7. As rotor 5 rotates within housing 5, the distance between the ends of slots 7 and the cylinder wall varies constantly. A complex system of ports and 22, 23 and channels 13-18 are machined into various components to apply pressure to the under side of rollers 8 to move them outwardly as the distance between the slot 7 and the cylinder wall increases, and to relieve fluid pressure under roller 8 as the distance between roller 7 and the cylinder wall decreases and roller 8 is forced into the slot. In this way, the effective diameter of the rotor 5 is varied during rotation. By rotating rotor 5 in the cylindrical housing, a somewhat pulsating flow of fluid is delivered to discharge port 10.
U.S. Pat. No. 3,160,147 to Hanson discloses a design for a rotary pump design in which a fluid refrigerant is compressed between a leading edge 36a of vane 30 and a first surface of abutment 51, and subsequently expanded between a trailing edge 36b of vane 30 and abutment 51. The outer end of vane 30 is sealed against the inner surface 14 of housing 11 by a roller 37 disposed within a recess 38. Vane 30 reciprocates within groove 27, and is urged outward by spring 41. In this way, the effective length of vane 30 is varied as rotor 25 is rotated within housing 11.
U.S. Pat. Nos. 3,171,589 to Cramer, 3,237,852 to Shaw, 3,891,355 to Hecht, and 4,743,176 to Fry disclose motor driven pumps which circulate working fluid as a coolant for the drive motor.
Eccentric rotor steam engine designs are disclosed in U.S. Pat. Nos. 581,265 to Bump, 607,684 to Draper, and 787,988 and 1,078,301 to Moore.
A need therefore exists for a compact, reliable fuel pump which delivers a continuous, smooth flow of fuel to the locomotive engine, and which exhibits lower capital costs, wear rates, and maintenance requirements.